Difference betwin 454?

[Hank70SS]

Originally Posted by earthquake68

Another thing to keep in mind is horse power ratings. In 1972 they rated gross horse power. That is, they measured the horsepower at the flywheel. Since you lose horsepower through the drive train, the numbers were misleading. In 1973, they switched to a net rating. They actually measured horsepower off the back wheels. This gave a much more realistic rating, albeit a depressing one. A 350 horse power car in 1972 was only rated at at say 290 in 1973 with no changes to the combination.

Primarily what changed was compression ratio dropped and cam profiles changed. GM opened up the combustion chambers and dropped lift and duration on the cam. Since a 454 bore and stroke remain constant, a new set of pistons, heads and cam will start pumping horse power like a big dog. None of this is easy, but it's definitely doable.

I think the change was to measure HP with standard accessories attached, still at the flywheel. Standard accessories being alternator, exhaust manifolds, etc. Prior to that HP was measured off a basically bare engine. I may be wrong though, that's just what I recall.